1. Field of the Invention
The present invention relates to plants that are stably infected with an endophyte fungus. The purpose in stably infecting plants with unique fungal endophyte is to import desired traits. These traits include no adverse effect on herbivore, insect resistance, drought tolerance and improved persistence in the plants. The plants, specifically grass without inoculation, with an endophyte would not evidence these traits as strongly as inoculated grasses. Endoophyte inoculated grasses can be used as turfgrass or foraging material depending on the grass type selected.
2. Description of Related Art
Grasses whether turf or forage, grow in various environmental conditions. Grass is subjected to such environmental stress such as drought, acid, basic and saline/sodic soil types, excessive water, frost and freezing temperatures, chemical applications and wide temperature changes. Additionally, grass is subjected to wounding stress. Grazing animals produce wounds as do insects, fungi, and nematodes and other predators. Considering these challenges it is surprising that grass is found world-wide, however, grass thrives world-wide because grass is adaptable. One of the adaptations a number of grasses have made is the positive association with fungal endophytes. Grasses exploit endophytes as a defence mechanism against a number of the adverse challenges listed above. Endophytes exploit grasses by obtaining nutrients from the grass host. Endophytes infecting the grass host provide a biological control system to the grass that reduces the damage of insect pests and diseases. When compared to the same uninfected grasses, improved drought tolerance and nitrogen use has been shown by endophyte infected grasses.
Neotyphodium and Epichloe endophytes occur in a number of different host grasses. These hosts include tall fescue, meadow fescue, fine fescues and ryegrasses. Many of the Neothyphodium endophytes produce alkaloids that are detrimental to herbivores. Cattle grazing on a tall fescue host infected with Neotyphodium coenophialum may suffer from fescue foot, fat necrosis or fescue toxicosis. The endophyte N. lolii in perennial ryegrass causes a neuromuscular disorder know as staggers in sheep, goats, horses, buffalo and deer. The endophyte that infects Achnatherium inebrians (drunken horse grass) causes horses and sheep to be intoxicated for up to 24 hours. The endophyte in sleepy grass (Stipe robusta) is held responsible for making animals suffer narcosis.
On the other hand, these same types of endophytes, provide beneficial effects to the grasses hosting them. For example, timothy (Phleum pratense) plants infected with the E. typhina endophyte resists leafspot fungus (Cladosporium pheli), tall fescue hosting N. Coenophialum is more resistant to Rhizoctonia zeae, and endophyte infected fine fescues show enhanced resistance to dollar spot (Sclerotinia homoeocarpa). In addition to increased disease resistance, benefits from endophyte infection include the host plants ability to withstand drought stress and resistance to insects. Many tall fescue infected by N. coenophialum show drought tolerance, increased herbage production and increased plant tillering. Decreased insect feeding is apparent in many turfgrass cultivars having a high percentage of Neotyphodium endophytes. Endophyte infected tall fescue resists feeding by billbugs, sod webworms, fall armyworms. Infected fine fescue resist feeding by hairy chinch bugs; and infected perennial ryegrasses resist feeding by: sod webworm, chinch bug, Argentine stem weevil, and billbugs.
Recently the relationship between symbiotic fungal endophytes and host grasses such as tall fescue (Festucae arundinacea Schreb.) perennial ryegrass (Lolium perenne L) and the fine fescues (Festuca spp.) has been the subject of research. Although this symbiotic relationship is beneficial to the grass and the endophyte, it is adverse to herbivores that are devouring the grass. Endophytes that associate naturally with perennial ryegrass, tall fescue and annual ryegrasses (Temulentumas multiflorum) as a host are known for producing toxicity in livestock.
The role between the health of a grazing animal and endophyte infection in the pasture grass was first noted by Bacon et al. Appl. Environ. Microbiol. 34 pg. 576-581 (1977). The outgrowth of this type of research led to the observation of the interactions between endophytes and grasses. In 1983 the U.S. Pat. No. 4,940,834 was filed on selected endophytes.
This patent relates specifically to the selection of the Lolium endophyte fungus (Epichloe typhina, Acremonium coenophialum). This patent taught the discovery that endophytes confer insect resistance and certain other performance enhancing traits on the natural host. The patent taught development of perennial ryegrass having a native endophyte capable of enhancing the performance characteristics of the host, crossing the ryegrass with paternal pollen and producing progeny containing the endophyte from the cross. Paired hybridisation or recurrent selection or multiple hybridisation was used to propagate the progeny plants. This patent did not provide a method of avoiding the herbivore toxicity problem associated with Lolium perenne L. hosted endophytes.
The PCT international application PCT US96/0927 published in December of 1996 described the introduction of endophytes into Bentgrass. Bentgrass does not, in its native state, support endophytes. The application teaches that by crossing uncultivated grass such as wild Bentgrasses that are native hosts to endophytes with native Bentgrasses (which are not native hosts) the cultivated Bentgrasses can be stably infected with the endophyte. In another aspect of the invention the inoculation of the plant tissue of a Bentgrass is taught.
There is an U.S. Pat. No. 5,723,720 issued Mar. 3, 1998 entitled, xe2x80x9cProcess for the development of endophyte-infected plantsxe2x80x9d. This patent describes infection of Bentgrasses and Kentucky grasses with endophytes.
Meadow fescue plants that were infected with N. uncinatum were shown to have the beneficial effect of better survival to certain diseases. The infected meadow fescue seedlings survived disease attack by Drechsiera sorokiniana and Rhizoctonia better than the non-infected seedlings. However, poorer survival was shown when the infected meadow fescue seedlings were infected by Fusarium culmorum than when the endophyte free seedlings were infected. This was reported in 1994 by Schmidt, D. Influence Of Endophytes Of Festuca Pratensis On Damping Off Diseases Of Seedlings. P. 267-273. In K. Krohn, etal. (etal. (ed.) Intl. Conf. On Harmful and Beneficial Micro. In Grassla. Pastures and Turf. Paderborn, Germany. The issue of herbivore toxicity was not the focus of this paper.